WASHINGTON — Associate Justice John Paul Stevens, the leader of the liberals on the Supreme Court, announced on Friday that he will retire at the end of this term, setting up a confirmation battle over his replacement that could dominate the political scene this summer.

In a brief letter to President Obama, whom he addressed as “my dear Mr. President,” Justice Stevens said he was announcing his retirement now because he had “concluded that it would be in the best interests of the Court to have my successor appointed and confirmed well in advance of the commencement of the Court’s next term” in October.

The retirement by Justice Stevens, 89, had been widely expected, because he did not hire the usual number of clerks for next year’s term.

The White House has been quietly evaluating potential nominees for months. Among those rumored to be in contention for the nomination are Solicitor General Elena Kagan and several appeals court judges, including Diane Wood and Merrick Garland.

A soft-spoken Republican and former antitrust lawyer from Chicago, Justice Stevens has been the leader of the liberal wing of a court that has become increasingly conservative. He was appointed by President Gerald Ford in December 1975 to succeed Justice William O. Douglas, who had retired the month before. He is the longest-serving current justice by more than a decade.

No doubt the Obama Administration has been considering replacements for Stevens for months now given all the speculation, but it’s worth noting that three weeks elapsed last year between Justice Souter’s retirement announcement and President Obama’s selection of Sonia Sotomayor to replace him. This time around, Obama has even more time to consider the nomination so we may have to wait awhile to see what they do.

As I’ve noted before, Justice Stevens is perhaps the most liberal member of the Court. Given that, it’s unlikely that whoever Obama appoints to replace him will have a significant impact on the ideological balance on the Court, except perhaps in close cases where a particularly persuasive Justice might be able to persuade a swing vote to accept his argument.

Nonetheless, given the political climate, the fact that this is an election year, and the record we already have from the Sotomayor hearings last year, I think we can expect that this while be a very politically charged nomination process. Although I don’t think there’s been a Supreme Court nominee since Bork that wasn’t politically charged.